Raised Garden Bed, building materials

First, remind me again why I should consider a garden?
To save hundreds of dollars on groceries. To eat substantially healthier and tastier foods than mass produced – genetically modified – prematurely harvested – irradiated foods. To learn a self reliant skill. Peace of mind. Therapy.

Second, what is the point of a raised garden bed?
They are a bit easier on the back when tending the garden. Raised garden beds are easier and simpler to manage from the perimeter. They enable addition of high quality soil mixtures. Oh, and some people like the looks of them.

A few choices of building materials for the structure of a raised garden bed include pressure treated lumber, cement blocks, or simply a perimeter of rocks, stone, or even logs.

PT Lumber for raised garden beds

Most all raised garden beds are built from lumber, that is, pressure treated lumber (PT). PT wood is ideal in any high moisture and/or ground contact installations.

Why use pressure treated lumber for raised garden beds?
It prevents rot and insects from prematurely destroying the wood.

What is pressure treated lumber?
Pressure treating is a process that forces a chemical preservative deep into the wood. The PT process starts with the wood being placed into a large cylindrical holding tank where much of the air is removed. Then the tank is filled with the preservative under high pressure, which forces it deep into the wood. The tank is then drained and the leftover preservative is reused.

Prior to 2003, the type of wood preservative that was used in residential and commercial structures included ‘arsenate’. It typically had a green hue to it. Due to health concerns, during 2003 the industry switched to a preservative with either copper or chromium. It typically has a dark brown hue to it. The ‘stuff’ comes off readily, so you will want to wear gloves…

Of importance to note is that this newer type of PT lumber requires the use of hot-dip galvanized or stainless steel hardware. Anything else will quickly corrode.

A good size PT lumber for garden beds is 2 in. x 12 in., the 12 inch height is plenty for the soil. Don’t be tempted to use 2 in. x 6 in. even though it costs less and may seem easier to deal with – it’s not tall enough to accommodate the amount of soil you will need. Other typical sizes include 2 x 8 or 2 x 10, which should be Okay for the depth of soil.

Concrete Block for raised garden beds

Although pressure treated lumber will last many years, a raised garden framed with cement blocks will essentially last forever.

It will be a bit more difficult to ensure a nice level top flat surface plane while placing the blocks to form a perimeter, and some people may not find the look as appealing as lumber, but it will last, and is a good alternative. One difference is that the typical concrete block is 8 inches tall, so the bed height will be a bit shorter than the wood framed example.

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2 Comments

Ken,
In regards to your recommendation for use of pressure treated lumber in a raised planter thought you might find this article interesting.http://www.toronto.ca/health/factsheet_ptw.htm
Personally I would use untreated cedar lumber, it won’t last as long (still a few years) and it can be a little more expensive, but you don’t have to worry about chemicals leaching into the soil.
The fact that they allow the use of the PT chemicals is baffling.
Near where I live in canada there was a train that derailed next to a recreational lake damaging tankers containing this chemical. (among others)http://www.tc.gc.ca/media/documents/rsa-lsf/wabamun.pdf
The cleanup took more than a year and still to this day you can find chemical slicks near the shores of the lake.

I use 2″ x 12″ untreated fir for my raised beds. I live in an extremely dry climate, so the wood actually lasts for 10-12 years. (The yellow jackets peel off the softer parts to build their nests, the nasty buggers!)
Tip for those of you who have burrowing rodents in your garden area: After constructing the wood frame for the raised bed, attach hardware cloth covering the bottom. Keeps those gophers out!